Device and method for detecting filter clogging

ABSTRACT

The invention relates to a device ( 1 ) and to a method for detecting filter soiling of a filter system consisting of at least an air filter ( 10 ) installed in an air duct ( 20 ) and an electrically controlled fan ( 30 ) for producing an air flow in the air duct ( 20 ), wherein the device ( 1 ) comprises at least a motor controller ( 40 ) for controlling the fan motor ( 31 ) by means of PWM control and an evaluating apparatus ( 50 ) for determining the actual rotational speed (n i ) of the fan ( 30 ) in accordance with the actual degree of modulation (T i ) of the motor current for achieving the present rotational speed (n i ), wherein, in the evaluating apparatus ( 50 ), setpoint value pairs (n setpoint , T setpoint ) for the setpoint rotational speed (n setpoint ) at a certain degree of modulation (T setpoint ) are also stored, as well as a comparator ( 51 ) ins order to compare the actual value pairs (n i , T i ) with the setpoint value pairs (n setpoint , T setpoint ) and to obtain the degree of filter soiling of the air filter ( 10 ) therefrom.

The invention relates to a device and to a method for detecting and measuring filter soiling.

In addition to fans, filters are typically used for air purification in ventilation systems. With many devices, the user cannot readily determine from the exterior whether the filter is already soiled or fraught with dirt particles such that it would have to be cleaned or replaced.

The determination and measurement of filter soiling in the prior art is implemented, e.g., with additional sensors or equipment such as, for example, with an infrared sensor for measuring filter soiling. With an infrared filter, the degree of soiling is measured, for example, in such a manner that an infrared light source is radiated into the filter and reflected back onto the opposite side by the reflector attached there, and measured. If the filter is only slightly soiled, much light is reflected; if it is extensively soiled, hardly any light appears at the measuring point. The electronic system calculates the degree of soiling from this difference in the radiation intensity. If no more light is reflected, the system also switches off, e.g., the current supply of the fan in the affected air duct.

A different method is the measurement of differential pressure upstream and downstream of the filter, wherein the differential pressure can be measured with increasing filter soiling thus providing conclusions regarding the degree of soiling. The disadvantage with this is that it requires additional measuring equipment, and the differential pressure can change based on other flow influences.

DE 4037685 A1 discloses a filter inspection device for the interior air filters of motor vehicles having an electric fan motor with a filter arranged in its suction area, an electronic fan motor rotational speed controller. The fan motor rotational speed controller and a climate-control unit are connected to outputs of a central control unit, by means of which an automatic filter inspection process can be implemented via a control program and at the inputs of which signal processing equipment as well as an in-rush current ammeter are connected via an analog/digital converter. To this end, separate measuring and control equipment is also necessary, which should be avoided simply for cost reasons.

The degree of filter soiling furthermore influences the required torque of the fan in a ventilation system such that the motor parameters must be permanently changed and the fan is also increasingly working in a suboptimal operating range.

Therefore, the object of the invention is to overcome the previously stated disadvantages and to provide a simple, cost-effective concept for detecting and/or measuring filter soiling, which can be implemented with a small number of components.

This object is achieved by the combination of features according to claim 1.

In a closed air flow channel or space, a fan such as, e.g., a radial fan establishes a pressure (“pressure accumulator”); in idle mode, this pressure can then release and thus act on the braking behavior of the fan. Depending on the degree of soiling and the air permeability of the filter, the pressure is more quickly or more slowly established and released.

A basic idea of the present invention is to provide a detection method for detecting filter soiling of an air filter in a flow range of a fan, with which the relation between the power consumption of the fan and its actual degree of modulation (PWM control) as well as the actual rotational speed can be used to draw a conclusion about filter soiling.

The determination of the power consumption of the fan can be compensated by a stored characteristic curve and thus made precise if an integrated measuring circuit is functioning too imprecisely. Upon its commissioning with a clean filter, the fan follows its fan characteristic curve and, in doing so, records a sufficient number of actual rotational speeds and actual degrees of modulation as value pairs. The measuring of a characteristic curve can alternatively take place by recording an existing characteristic curve, e.g., by means of a data bus, in that data, from a database, suitable according to the installation situation and the selected filter type can be used.

In addition, in a preferred embodiment according to the method according to the invention, the intermediate circuit voltage and the intermediate circuit current are recorded. These data are stored in a fan memory and a conclusion about filter soiling can be drawn directly therefrom.

A positive side effect of the method according to the invention is that the aging process of the fan is slowed. Aging refers, for example, to the wear of the bearing, for which there are currently already corresponding service life calculation models. Alternatively, parameters determining bearing service life can also be measured by means of corresponding sensors.

With the method according to the invention, the fan compares the current actual rotational speed and the actual degree of modulation in ongoing operation to the corresponding stored setpoint data. According to the invention, a comparison of value pairs thus takes place. If a stored degree of modulation according to a stored rotational speed value deviates from the current actual degree of modulation of the current actual rotational speed value by more than a specified permissible deviation value, this condition is evaluated as filter soiling, because the degree of modulation must be increased with filter soiling in order to reach the desired rotational speed that would be present with a non-soiled or only slightly soiled filter.

By means of recording the interim circuit voltage and the interim circuit current, it is possible to further ensure the method and to determine whether the deviation is not from the fan (e.g. bearing damage) or originates from the control circuit for the fan. According to the invention, a tolerance range with maximum values and minimum values is defined for the degree of permissible deviation.

The report of a soiled filter can take place as a warning on the bus, as a flashing code of an LED, or as a set fault signal relay. The fault signal can also be generated externally by means of a suitable interface.

Due to the method according to the invention, a complex and possibly vulnerable sensor system, which is additionally cost-increasing, is superfluous. In contrast, the solution according to the invention only provides an evaluation unit, in which relations between the rotational speed and the degree of modulation are used, as well as optionally also the interim circuit voltage and the interim circuit current.

According to the idea of the invention, the degree of soiling can be calculated when the deviation of the actual values from the setpoint values has a linear character and the absolute deviation is determined. The value determined in this manner can be queried via a data bus or may be present as an analog voltage signal on a signal output. Preferably, a low voltage would be evaluated as minimal soiling and a maximum permissible voltage of the analog signal would be evaluated as maximally permissible soiling.

The time-discrete or continuous recording of the values over time can likewise be evaluated and a gradual change in filter soiling up to a maximum permissible degree of soiling can also be detected from the derivation according to time. If the first derivation according to time is somewhat constant in this case, continuous and increasing filter soiling can be derived therefrom.

In an alternative embodiment of the invention, it may be provided to reverse the rotational direction of the fan for a defined time and, in doing so, the actual degree of modulation, the actual rotational speed, and the intermediate circuit current and the intermediate circuit voltage are continuously recorded.

In this case, the change rate of the PWM signal while blowing the filter clear is evaluated during reverse operation, wherein, by incorporating the specific parameters of the fan, the circumstance in which fan wheels are typically technically optimized based on a forward rotational direction and the fans in the reverse rotational direction thus only achieve a limited air performance is compensated.

According to the invention, a rotational speed jump to the fan is provided, and its jump response recorded and evaluated, in a further embodiment. The filter functions as a lowpass in this case. The output characteristic variable here is the actual PWM signal. If the filter is just slightly soiled, it subsides very quickly; if the filter is greatly soiled, it subsides only slowly. Thus, the change rate of the actual PWM is considered. This embodiment is similar to the previously mentioned method of the reverse operation except that no compensation must be made for the poorer air performance of the fan wheels in reverse operation.

In a further embodiment of the invention, the filter is additionally described by mathematical parameters in a model. The jump response provides actual values of these parameters, which are then compared with the ideal values from the model. Such filter parameters can be obtained, inter alia, by means of Kalman filters or other gradient methods. An evaluation of the tendency over time also takes place here.

A further embodiment of the invention provides that the fan can be used as a loudspeaker with the assistance of its blades due to a precise modulation of the motor current with a sinusoidal carrier signal known in phase and amplitude. It is the property of a loudspeaker that it can also receive oscillations, i.e. tones. The tones received by the ventilator are then expressed as changes in the motor current provided that a phase displacement and amplitude reduction occur in the motor current for the generated signals. A filter then dampens these ultrasound signals as a function of its soiling such that the received signal provides information on the degree of soiling both in amplitude and in the phase position. The evaluation of the signals in the current of the fan motor can take place, for example, by correlating the transmitted signals with the received signals. Interfering signals in this case can also be hidden by means of a variation in the transmit frequency.

Other advantageous further embodiments of the invention are characterized in the dependent claims and/or are shown in more detail in the following by means of the figures, along with the description of the preferred embodiment of the invention.

The following is shown:

FIG. 1 a schematic view of a device according to the invention; and

FIG. 2 a schematic representation of the steps of the method according to the invention;

The invention is described in the following using an exemplary embodiment, wherein use of the same reference characters indicates the same structural and/or functional features.

FIG. 1 shows a schematic view of an exemplary embodiment of a device 1 for detecting filter soiling in the filter system 2, wherein the filter system 2 consists of at least an air filter 10 installed in an air duct 20 and an electrically controlled fan 30 creating an air flow in the air duct 20. The device 1 has a motor controller 40 for controlling the fan motor, wherein a PWM control 32 is provided for regulating rotational speed. Furthermore, an evaluating apparatus 50 for determining the actual rotational speed n_(i) of the fan 30 as a function of the actual degree of modulation (duty cycle) of the engine current is provided for achieving the current rotation speed n_(i).

Furthermore, setpoint value pairs n_(setpoint), T_(setpoint) for the setpoint rotational speed n_(setpoint) of the filter system 2 at a certain degree of modulation T_(setpoint) are stored in the evaluating apparatus 50. Moreover, a comparator 51 is provided in the device in order to compare the respective actual value pairs n_(i), T_(i) with the stored setpoint value pairs n_(setpoint), T_(setpoint) and from that determine the degree of filter soiling of the air fan 10. As soon as the deviation is greater than a specified limit value in a tolerance range, a signal is output to the LED light 61 via the interface 60, which indicates impermissible filter soiling.

FIG. 2 shows a schematic representation of the steps of the detection method according to the invention for determining filter soiling of a filter system, which can be implemented with the device according to FIG. 1. The following steps are provided with the method.

First, the recording or transmission of the motor characteristic curve related to the rotational speed as a function of the degree of modulation in the filter system 2, in which the air filter 10 is not soiled, thus, e.g., during system startup or a filter replacement, takes place in one step 100.

These value pairs are stored as setpoint value pairs n_(setpoint), T_(setpoint) in a data memory of the device 1 in step 110.

During system operation, the respective determination of the actual rotational speed n_(i) of the fan 30 and of the actual degree of modulation T_(i) of the motor current takes place to achieve the current actual rotational speed n_(i) in a step 120.

In a further step 130, there is a comparison of the actual value pairs n_(i), T_(i) with the stored setpoint value pairs n_(setpoint), T_(setpoint) with the comparator 51 of the device 1.

Subsequently, in step 140, the determination takes place as to whether the determined deviation of the actual value pairs n_(i), T_(i) from the setpoint value pairs n_(setpoint), T_(setpoint) exceeds a maximum predefined deviation. The deviation in this case can be determined as a range deviation in a permissible tolerance range, wherein either the rotational speed at a certain power consumption and thus a certain duty cycle is too low or whether an excessively high duty cycle is required in order to achieve a certain rotational speed. In particular, when the deviation of the actual values from the setpoint values has a linear characteristic over time, not only the current filter clogging but also the time of the maximally permissive soiling, at which a filter change should take place, can be predicted from the increasing deviation. 

1. A device for detecting filter soiling of a filter system having at least an air filter installed in an air duct and an electrically controlled fan for producing an air flow in the air duct, wherein the device comprises at least a motor controller for controlling a fan motor by means of pulse width modulation (PWM) control and an evaluating apparatus for determining an actual rotational speed (n_(i)) of the fan in accordance with an actual degree of modulation (T_(i)) of the motor current for achieving the actual rotational speed (n_(i)), wherein, in the evaluating apparatus, setpoint value pairs (n_(setpoint), T_(setpoint)) for a setpoint rotational speed (n_(setpoint)) at a setpoint degree of modulation (T_(setpoint)) are also stored, as well as a comparator which is formed to compare the actual value pairs (n_(i), T_(i)) with the setpoint value pairs (n_(setpoint), T_(setpoint)) and to obtain a degree of filter soiling of the air filter therefrom as well as from an intermediate circuit voltage and an intermediate circuit current.
 2. A detection method for determining filter soiling of a filter system having at least an air filter installed in an air duct and an electrically controlled fan for producing an air flow in the air duct, wherein a motor controller and an evaluating apparatus are provided, having the following steps: a. determining an actual rotational speed (n_(i)) of the fan, b. determining an actual degree of modulation (T_(i)) of the motor current in order to achieve the actual rotational speed (n_(i)), c. comparing the actual value pairs (n_(i), T_(i)) with stored setpoint value pairs (n_(setpoint), T_(setpoint)), d. determining whether a deviation of the actual value pairs (n_(i), T_(i)) from the setpoint value pairs (n_(setpoint), T_(setpoint)) exceeds a maximum predefined deviation, e. recording an intermediate circuit voltage and an intermediate circuit current, and f. evaluating the deviation of the actual value pairs (n_(i), T_(i)) from the setpoint value pairs (n_(setpoint), T_(setpoint)) as well as from the intermediate circuit voltage and from the intermediate circuit current to obtain a degree of filter soiling.
 3. A detection method with a device according to claim 1, wherein the degree of filter soiling is obtained from the power consumption of the fan motor without using sensors in that the actual power consumption, which can be determined by the actual value pairs (n_(i), T_(i)), is compared to a defined setpoint power consumption of the unsoiled filter system in the comparison, which can be determined by the setpoint value pairs (n_(setpoint), T_(setpoint)), wherein the intermediate circuit voltage and the intermediate circuit current are recorded and used in the evaluation of the degree of filter soiling.
 4. The detection method according to claim 3, having the following steps: a. determining the actual rotational speed (n_(i)) of the fan, and b. determining the actual degree of modulation (T_(i)) of the motor current in order to achieve the actual rotational speed (n_(i)), and c. comparing the actual value pairs (n_(i), T_(i)) with stored setpoint value pairs (n_(setpoint), T_(setpoint)), and d. determining whether a deviation of the actual value pairs (n_(i), T_(i)) from the setpoint value pairs (n_(setpoint), T_(setpoint)) is within or outside the maximum predefined deviation
 5. The detection method according to claim 4, wherein the evaluation of the degree of filter soiling takes place from the power consumption of the fan and by means of a stored fan characteristic curve.
 6. The detection method according to claim 3, wherein a reporting of a soiled air filter is output as a signal when the maximum deviation of the actual values from the setpoint values is exceeded.
 7. The detection method according to claim 3, wherein the direction of rotation of the fan is reversed for a defined time as compared to the proper rotational direction and, in doing so, the actual degree of modulation, the actual rotational speed, and the intermediate circuit current and the intermediate circuit voltage are continuously recorded.
 8. The detection method according to claim 3, wherein a jump in rotational speed is preferably initiated by means of a motor controller with the fan, and its jump response is recorded and evaluated.
 9. The detection method according to claim 2, wherein a reporting of a soiled air filter is output as a signal when the maximum deviation of the actual values from the setpoint values is exceeded.
 10. The detection method according to claim 2, wherein the direction of rotation of the fan is reversed for a defined time as compared to the proper rotational direction and, in doing so, the actual degree of modulation, the actual rotational speed, and the intermediate circuit current and the intermediate circuit voltage are continuously recorded.
 11. The detection method according to claim 2, wherein a jump in rotational speed is preferably initiated by means of a motor controller with the fan, and its jump response is recorded and evaluated.
 12. The detection method according to claim 2, wherein the degree of filter soiling is obtained from the power consumption of the fan motor without using sensors in that the actual power consumption, which can be determined by the actual value pairs (n_(i), T_(i)), is compared to a defined setpoint power consumption of the unsoiled filter system in the comparison, which can be determined by the setpoint value pairs (n_(setpoint), T_(setpoint)). 